1. Field of the Invention
The present invention relates to a method and an apparatus for analyzing the concentration of materials in a suspension, and in particular to an analysis method and an analysis apparatus that are appropriate for analyzing the concentration of materials in a suspension with high turbidity, such as the analysis of the amount of lipids in milk, the concentration of vegetable juice, or the concentration of microscopic algae (so-called phytoflagellates) that float in water.
2. Description of Related Art
A Gerber method and a Babcock method have been used for the conventional measurement of the amount of lipids (butterfat) that are contained in milk or processed milk (they are generally referred to as milk in the present specification). According to both of these methods, concentrated sulfuric acid is added to milk so as to break the globule membrane that surrounds the milk fat, and then, droplets of milk fat that float in the concentrated sulfuric acid solution are collected through centrifugal separation, and thus, the volume is measured.
In place of these conventional techniques, a method for measuring the amount of lipids using near-infrared spectrometry has been put into practice. In accordance with this method for measurement using near-infrared spectrometry, milk is contained in a sample cell for measuring a liquid sample, and the sample cell is irradiated with light for measurement so that the transmitted light is detected to measure the absorption spectrum of the milk. After that, the amount of lipids in the milk to be measured is calculated from a measurement model that has been prepared in advance by measuring the absorption spectra of a number of types of milk, of which the amount of lipids are already known.
An online measuring method has also been proposed as a method for measuring the amount of lipids in milk using near-infrared spectrometry (see Non-Patent Document 1). In accordance with this technology, a sample chamber through which milk flows is irradiated with light from a halogen lamp so that spectrometry is carried out after guiding the diffuse transmission light to a spectrometer from milk through an optical fiber. The absorption spectrum of light from the milk that flows through the sample chamber is continuously measured so that the amount of lipids in the milk that flows through the sample chamber is sequentially measured online on the basis of the measurement model that has been prepared in advance.